REGULATION OF FOOD AND WATER INTAKE 353 



the food did not pass through the mouth or pharynx. And at the end of this 

 period, intake was not depressed by quinine adulteration. Taken together, 

 these two facts make it virtually certain that the food did not stimulate any 

 of the receptors in the olfactory mucosa or the oral pharynx during the act 

 of ingestion. 



Clearly, the central neural mechanism controlling food intake can operate 

 effectively without receiving sensory information about the taste and smell 

 of the food being ingested, or its feel in the mouth, and without proprio- 

 ceptive feedback from the muscles involved in chewing and swallowing. 

 Metering by mouth provided by the act of eating is not necessary for the 

 regulation of food intake in the normal rat. Post-ingestion factors such as 

 sensations from the gut and chemical or thermal changes in the blood 

 reaching the central nervous system must be sufficient to control the onset 

 of feeding, the size of individual meals, the total amount of food eaten 

 during a single day and for longer periods of time up to more than a month. 

 Since drinking has previously been shown to be similarly independent of 

 oro-pharyngeal and olfactory sensations (Epstein, 1960), these considera- 

 tions apply to drinking as well as feeding. 



All of the above applies to the caged animal. Clearly, sensations from 

 the mouth, olfactory mucosa and pharynx are of great importance for the 

 management of consummatory behavior in the wild, where the animal 

 must detect food in the environment, discriminate between the edible and 

 inedible, and reject poisons. Specific hungers, such as the increased intake 

 of salt that follows adrenalectomy also depend upon the animal's capacity 

 to taste (Richter, 1956). What we are emphasizing is that although oro- 

 pharyngeal sensations are essential when the animal must find food and 

 identify it, they are not essential when the animal's only problem is how 

 much to eat. 



THE ROLE OF TASTE AND SMELL IN THE REGULATION OF 

 FOOD INTAKE IN ANIMALS WITH HYPOTHALAMIC DAMAGE 



But all these conclusions about the role of taste and smell in the regula- 

 tion of food and water intake are based on the study of normal animals. 

 And every study of regulation assumes normal motivation for food and water. 

 It is taken for granted that if an animal does not eat, or does not regulate 

 adequately, it is because regulation is impaired. We shall now attempt to 

 show that regulation depends critically on the existence of a powerful urge 

 to eat or drink. In normal animals, this urge overcomes all barriers to 

 ingestion and makes taste appear trivial. But regulation cannot exist 

 without adequate motivation. In brain-damaged animals, where motiva- 

 tion is impaired, taste becomes critical for regulation. We will show that 

 taste and smell are powerful motivating stimuli — psychic energizers — that 



